Highly Selective Electrocatalytic CuEDTA Reduction by MoS2 Nanosheets for Efficient Pollutant Removal and Simultaneous Electric Power Output

Highlights Highly efficient CuEDTA removal by an electrolyzer with MoS2 nanosheet cathode. Higher removal rate and Faraday efficiency compared with other widely reported electrocatalytic technologies. CuEDTA/Zn primary battery is constructed for the first time to realize CuEDTA removal and synchronous power generation. Supplementary Information The online version contains supplementary material available at 10.1007/s40820-023-01166-7.


Text S1 Thermodynamics of Electrode Process
Firstly, it should be noted that the "CuEDTA" is an acronym, not the actual form of it in the aqueous solution. With different pH, there is an ionization equilibrium between CuEDTA 2-, CuEDTAH -, and CuEDTAH2 in the solution [S1]. According to the basic principles of electrochemistry, the standard equilibrium potential of the reaction (CuEDTAH2 + 2e = Cu +H2EDTA) can be calculated by the following equation: where ′ represents the standard electrode potential of redox electricity on Cu 2+ /Cu (0.34V), R is the ideal gas constant, T is the thermodynamic temperature, n is the number of reacting electrons, F is Faraday constant, and is the dissociation equilibrium constant of CuEDTAH2 (10 -18.7 ). It can be calculated that at 25 ℃, the standard electrode potential of CuEDTAH2 reduction is -0.212 V, which means that the standard electrode potential is lower than that of hydrogen evolution reaction (0 V). Therefore, the CuEDTA reduction is inevitably accompanied by the process of hydrogen evolution, and highly selective catalyst for CuRR is preferred to enhance the efficiency of CuEDTA reduction.

Text S2 Material Characterizations
X-ray diffraction (XRD) test was performed to characterize the crystal structure of the prepared samples on a Bruker D8 Advance X diffractometer. The size and surface morphologies of the samples were studied by scanning electron microscope (Hitachi S-S2/S11 4800 SEM) with energy dispersive X−ray spectroscopy (EDS). The high-resolution transmission electron microscope images and selected area electron diffraction (SAED) patterns were obtained by transmission electron microscopy (TEM, JEM−2100) at 200 kV. The chemical composition was studied by X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250Xi) with Mg Kα radiation source (hν = 1253.6 eV). The position of the C1s peak at 284.8 eV was employed to calibrate the position of binding energies. The phases of MoS2 were studied by Raman spectroscopy (HORIBA HR Evolution Raman spectrometer with 532 nm laser excitation).

Text S3 Electrochemical Tests
All electrochemical measurements including CuRR and HER were conducted on a CHI 760E electrochemical workstation equipped with rotate disk electrode device in a threeelectrode cell at room temperature. Pt wire and saturated calomel electrode (SCE) was used as the counter and reference electrode, respectively. The MoS2 nanosheet electrode was prepared by dropping 5 µL of 1 mg/mL MoS2 nanosheet dispersion on the glassy carbon electrode (diameter = 3 mm). The commercial 20% Pt/C, Cu nanoparticle, and carbon black (CB) was loaded on the glassy carbon (GC) electrode with the mass loading of 0.71 mg/cm 2 . Linear scanning voltammetry (LSV) and cyclic voltammetry (CV) were measured at a scan rate of 5 mV/s and 100 mV/s in 10 mM CuEDTA and 0.5 M NasSO4 solution in Ar, respectively. The electron transfer number of the reaction was calculated using the following equation: = 0.62 2/3 −1/6 1/2 0 where is the mass transfer limit current, n is the electron transfer number, F is the Faraday constant (96485 C/mol), D is the diffusion coefficient of CuEDTA (about 7.5*10 -6 cm 2 /s), is the kinematic viscosity of solution (0.01 cm 2 /s), is the rotational angular velocity, and 0 is the reactant concentration (0.01 M). The electron transfer number of the reaction can be obtained by linear fitting of the mass transfer limiting current density at different rotational angular velocity.

Text S4 Calculation of Special Removal Efficiency, Faraday Efficiency (FE), and Cumulative Output Energy (COE)
In the current research on the removal of CuEDTA by electrochemical method, there is no clear kinetic order for the removal rate of CuEDTA. Therefore, the specific removal rate defined by us is the removal amount of CuEDTA per unit area within a certain time.
The Faraday efficiency was calculated by the following equation: where q, I, and t is the theoretical amount of electric charge required for CuEDTA reduction, current of the electrochemical system, and time.

S3/S11
The cumulative output energy in the battery was calculated by the following equation: where U is the voltage recorded in chronopotentiometry method.

Text S5 Rate-limiting Step Analysis
The kinetics of the CuEDTA electroreduction process depends on the rate-limiting step. These electrode processes include reactant diffusion, pre-conversion, electron transfer ( 2+ + 2 = ) and so on. Under good mass transfer conditions, pre-conversion is usually the primary rate-limiting step. Decomplexation involves the breaking of multiple chemical bonds, and the activation energy of one of these steps is typically hundred kilojoules per mole. As for the electron transfer reaction that involves the electron transfer steps, its activation energy is influenced by the overpotential: where ∆ ≠ and ∆ ≠ is activation energy of non-standard and standard states, is transfer coefficient, F is Faraday constant, and ∆ is overpotential. The more negative the cathode overpotential, the smaller the activation energy of the cathode reaction and the faster the intrinsic rate will be. Therefore, under the reduction condition of CuEDTA ( ( / ) = −0.21 ), the overpotential of the electron transfer step is in strongly polarized region ( ( 2+ / ) = 0.34 ). The activation energy of the Cu 2+ gaining electrons is much less than that of the decomplexation step under the condition of strong polarization. Therefore, we speculate that the rate-limiting step is decomplexation rather than electron transfer.

Text S6 DFT Calculation
The present first principle DFT calculations are performed by Vienna Ab initio Simulation Package (VASP) [S2] with the projector augmented wave (PAW) method. The exchange-functional is treated using the generalized gradient approximation (GGA) of Perdew-Burke-Emzerhof (PBE) functional. The energy cutoff for the plane wave basis expansion was set to 450 eV and the force on each atom less than 0.03 eV/Å was set for convergence criterion of geometry relaxation. Grimme's DFT-D3 methodology [S3] was used to describe the dispersion interactions. Partial occupancies of the Kohn−Sham orbitals were allowed using the Gaussian smearing method and a width of 0.05 eV. The Brillourin zone was sampled with Monkhorst mesh 3×3×1 through all the computational process. The self-consistent calculations apply a convergence energy threshold of 10 -5 eV. A 15 Å vacuum space along the z direction was added to avoid the interaction between the two neighboring images. In the DFT calculation, because the interaction between Cu and EDTA is too strong, we added an H + to each step of dissociation process, so the energy of the final state is lower than that of the beginning state. Fig. S1 The calibration curve of CuEDTA concentration determined by HPLC